This invention relates to an improved substage illuminator for use with optical inspection systems, and more particularly for use with variable magnification telecentric systems.
In a microscope system, as distinguished from gaging systems for inspecting workpieces, and the like, the object plane is essentially fixed, so that a substage collimator typically consists of an illumination source focused on the thin object that is being observed by the microscope. Usually a field stop aperture is provided near the object, while an adjustable iris at the lens serves to adjust the F-number of illumination to match the magnification in use. This can then provide the proper angular range of illumination for best imaging, while minimizing over-exposure and heating of biological specimens.
However, in gaging applications the location of the object that is being inspected is allowed to vary over a considerable range, and the effects of improper collimation are more problematical due to a condition referred to as xe2x80x9cwall-effectxe2x80x9d. For example, when viewing objects such as cylinders lying in the focal plane, the image of the sides of the object is confounded because of obstruction of the illumination and imaging cones of light, while distorted images of the substage illuminator reflected off of the object""s sides create inaccuracies. It has been discovered that these effects are minimized when the substage illuminator is designed to exactly fill the aperture of the magnification system in use, where a variety of magnifications and F-numbers are available. An improved substage illuminator of the type described would be particularly suitable for use in connection with inspection apparatus as disclosed in U.S. Pat. No. 5,668,665 which describes a system offering a variety of magnifications, and also the continuous zoom system disclosed in U.S. Pat. No. 5,523,583, both of which patents are owned by the assignee of the instant invention.
In each of the two above-noted U.S. patents the work that is to be inspected or gaged is mounted on a work support beneath the objective lens and surface illuminator of the optical inspection apparatus and in registry with a central opening or transparent section of the work support. Positioned beneath the work support is a conventional substage light source which is disposed to project illumination through the work support onto the underside of the workpiece, while the upper side of the workpiece may also be illuminated by surface illuminator portions of the apparatus. As noted above, among the problems associated with conventional substage illuminators is the fact that imaging cones of light from the substage illuminator are reflected from the sides of the inspected object, particularly cylindrically shaped objects, thereby creating inaccuracies in the gaging thereof.
It is an object of this invention, therefore, to provide an improved substage illuminator, which is particularly suitable for use with optical inspection apparatus for any type which is adjustable to provide therefor a variety of magnifications and F-numbers.
A more specific object of this invention is to provide for adjustable optical inspection apparatus of the type described, an improved substage illuminator having means for controlling its light source diameter, thereby exactly to fill the aperture of the optical inspecting apparatus for any number of different magnifications and F-numbers thereof.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.
The substage illuminator contains or has connected thereto a light source for projecting a circular beam of light out of an opening in the housing to the underside of a workpiece, which is positioned beneath the inlet aperture of variable magnification apparatus that is employed for inspecting and gaging the workpiece. The diameter of the beam produced by the light source can be adjusted to compensate for any changes in the F/number or magnification of the associated gaging apparatus. The diameter can be made adjustable by employing as a light source a plurality of radially spaced circular arrays of light emitting diodes, the arrays of which can be selectively energizable to produce a circular beam of the desired diameter, or the source can comprise a circular L.C.D. aperture generator, which also can be operated to emit beams of light of selectively different diameters. In either case the beams of light are passed through a collimating lens which is secured over the light emitting end of the housing beneath an anti-glare filter. To permit even further adjustment of the diameter of the light beam emitted by the light source, an adjustable iris diaphragm is mounted in the housing between the light source and the collimating lens. The light source may also comprise a fiber optics conductor producing a circular beam of light which is transmitted successively through a light shaping diffuser and adjustable iris diaphragm, which are interposed between the light source and the collimating lens. In each embodiment the diameter of the light beam emitted from the housing can be adjusted to fill the inlet aperture of the optical gaging apparatus in order to compensate for any change in the magnification and F/number of the inspection apparatus.